1. Field of the Invention
The present invention relates to a lighting device, and to a document scanning device including the lighting device.
2. Description of Related Art
A document scanning device has a lighting device that illuminates a document face. Conventionally, such a lighting device uses a fluorescent tube such as a CCFL (cold-cathode tube) as its light source. In recent years, an LED has become common in view of saving energy.
In such an LED-type lighting device, heat generated by the LED becomes significant, as the brightness increases. So, the heat has to be radiated into the air in order to avoid overheating of the LED, breaking down of a wire, and so on. To radiate the heat, a metal housing with a high heat conductivity is used in Related Art 1. In this Related Art, the heat generated by the LED is transmitted to the housing and the housing radiates the heat into the air.
Related Art 1: Japanese Patent Application Publication No. 2006-269140
However, when the temperature of the housing itself increases, it can not radiate the heat very well. To raise radiation performance, a heat radiator that radiates a part of the heat may be provided separately from the housing. Still, when the temperature of the heat radiator increases, the heat radiator can not radiate the heat very well. Consequently, sufficient radiation performance can not be ensured.